A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, e.g. a mask/reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. comprising part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is generally via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. Often, a single substrate will contain a network of adjacent target portions that are successively patterned. Examples of lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
In a lithographic apparatus, the substrate table is generally constructed to hold a substrate of only a particular “standard”. dimension, e.g. a 200 mm wafer, as this allows the substrate table's design to be optimized for the particular substrate. Various other types of substrate supporting tables, such as found in auxiliary apparatus, substrate handling components, substrate transport devices, etc., are also often designed to handle substrates of a standard size and shape.
However, there are occasions when it is desirable to process a substrate that is either not of a standard size or not of a standard shape. For example, certain substrates, such as InP, GaAs and SiC substrates often have dimensions that are too small for common substrate tables. Also, substrates may have different shapes than the standard. For example, although wafers are often rounded or may be rounded with a flat portion along part of the circumference, other shapes such as squares, rectangles and quarters of a rounded substrate of various sizes may be desirable. Moreover, it may be desirable to process irregular shapes, each of which may be unique, for example, as a result of breakage of a larger substrate into irregular pieces. However, it is relatively cumbersome and expensive to design and build a substrate table tailored to such non-standard substrates. Further, a user may desire to use a single lithographic apparatus to be able to expose a variety of substrates, e.g. both “standard” and “non-standard” substrates.
Furthermore, employing a non-standard substrate in a lithography apparatus designed for a particular standard substrate may raise concerns regarding adequately leveling the non-standard substrate.
Objectives include providing methods and substrate holders alleviating one or more of the above-noted problems.
Substrate holders are mentioned in, for example, U.S. Pat. Nos. 6,583,858 and 6,822,730, and in co-pending U.S. application Ser. No. 11/170,735.